[asterisk-users] TCP port, VPN and resolving the cutting voice problem

[Jeff LaCoursiere]

On Tue, 30 Nov 2010, Steve Jones wrote:

> Just the contrary - Most QoS schemes will drop TCP first, specifically because it is known that with TCP, the
> packet will be resent, so no application will be hurt.  UDP is not dropped first because it is known that there
> will likely be more impact.
> 
> I am not aware of any way to run IAX over TCP, and I agree it would be a bad idea.  The proper thing to do is to
> implement PROPER QoS on BOTH SIDES of the link, which I hope is point to point.  If it goes over the Internet,
> your QoS is lost as soon as it hits a router you dont control (or pay for QoS services on)
> 
> I think in IAX, the jitter buffer size can be adjusted, but I dont know the detail on this..  A jitter buffer can
> be looked upon as like a funnel - as packets arrive, they are dumped in the funnel, which is then pouring your
> audio out the bottom in a smooth stream, no matter how much delay there is in the filling of the funnel.   When
> the funnel runs out of packets (ie: delay has caused you to run out of data) then you get a break in your audio
> stream.  Increasing the jitter buffer (bigger funnel) can fix this, but at a certain point, the audio will be SO
> DELAYED (because the packets are waiting in the buffer) that the users will notice and get confused.
>

Just want to point out that a jitterbuffer will do NO GOOD if packet loss 
is occurring.  Proper QoS on both ends is ideal of course, but I have seen 
some pretty clever ideas employed on the CPE side of link to effectively 
provide QoS in both directions, when you have no control over your ISPs 
routers.  For example - you can effectively control the inbound flow of a 
TCP based application by delaying the ACKs sent back to the content 
provider.  Doesn't help you with UDP streams though, unfortunately.

j

> 
> 
> -Steve
> 
> 
> 
> ---------original message ------
> 
> From: "Mike" <list at net-wall.com>
> To: "'Asterisk Users Mailing List - Non-Commercial Discussion'" <asterisk-users at lists.digium.com>
> Date: Tue, 30 Nov 2010 12:34:08 -0500
> Subject: Re: [asterisk-users] TCP port, VPN and resolving the cutting voice problem
> 
> > I know understand the latency due to the resending .. But if the link was
> have a good speed internet, then resending will make a big latency?
> 
> I think the point is that with TCP, congestion will create a vicious circle
> of more congestion, while with UDP congestion is bad in itself, but doesn't
> result in more congestion created by the original congestion.
> 
> That being said, isn't UDP sometimes looked at as being lower priority than
> TCP by many routers out there and dropped first when congestion does occur?
> That makes it a good reason to use TCP in some cases.
> 
> Mike
> 
>